Enhance model and service documentation with detailed comments and descriptions

- Updated Group, Trip, User, and other model classes to include comprehensive documentation for better understanding and maintainability.
- Improved error handling and logging in services, including AuthService, ErrorService, and StorageService.
- Added validation and business logic explanations in ExpenseService and TripService.
- Refactored method comments to follow a consistent format across the codebase.
- Translated error messages and comments from French to English for consistency.

lib/models/expense.dart

@@ -3,47 +3,109 @@ import 'package:equatable/equatable.dart';
 import 'package:flutter/material.dart';
 import 'expense_split.dart';
 
+/// Enumeration of supported currencies for expenses.
+/// 
+/// Each currency includes both a display symbol and standard currency code.
 enum ExpenseCurrency {
+  /// Euro currency
   eur('€', 'EUR'),
+  /// US Dollar currency  
   usd('\$', 'USD'),
+  /// British Pound currency
   gbp('£', 'GBP');
 
   const ExpenseCurrency(this.symbol, this.code);
+  
+  /// Currency symbol for display (e.g., €, $, £)
   final String symbol;
+  
+  /// Standard currency code (e.g., EUR, USD, GBP)
   final String code;
 }
 
+/// Enumeration of expense categories with display names and icons.
+/// 
+/// Provides predefined categories for organizing travel expenses.
 enum ExpenseCategory {
+  /// Restaurant and food expenses
   restaurant('Restaurant', Icons.restaurant),
+  /// Transportation expenses
   transport('Transport', Icons.directions_car),
-  accommodation('Hébergement', Icons.hotel),
-  entertainment('Loisirs', Icons.local_activity),
+  /// Accommodation and lodging expenses
+  accommodation('Accommodation', Icons.hotel),
+  /// Entertainment and activity expenses
+  entertainment('Entertainment', Icons.local_activity),
+  /// Shopping expenses
   shopping('Shopping', Icons.shopping_bag),
-  other('Autre', Icons.category);
+  /// Other miscellaneous expenses
+  other('Other', Icons.category);
 
   const ExpenseCategory(this.displayName, this.icon);
+  
+  /// Human-readable display name for the category
   final String displayName;
+  
+  /// Icon representing the category
   final IconData icon;
 }
 
+/// Model representing a travel expense.
+/// 
+/// This class encapsulates all information about an expense including
+/// amount, currency, category, who paid, how it's split among participants,
+/// and receipt information. It extends [Equatable] for value comparison.
 class Expense extends Equatable {
+  /// Unique identifier for the expense
   final String id;
+  
+  /// ID of the group this expense belongs to
   final String groupId;
+  
+  /// Description of the expense
   final String description;
+  
+  /// Amount of the expense in the original currency
   final double amount;
+  
+  /// Currency of the expense
   final ExpenseCurrency currency;
-  final double amountInEur; // Montant converti en EUR
+  
+  /// Amount converted to EUR for standardized calculations
+  final double amountInEur;
+  
+  /// Category of the expense
   final ExpenseCategory category;
+  
+  /// ID of the user who paid for this expense
   final String paidById;
+  
+  /// Name of the user who paid for this expense
   final String paidByName;
+  
+  /// Date when the expense occurred
   final DateTime date;
+  
+  /// Timestamp when the expense was created
   final DateTime createdAt;
+  
+  /// Timestamp when the expense was last edited (null if never edited)
   final DateTime? editedAt;
+  
+  /// Whether this expense has been edited after creation
   final bool isEdited;
+  
+  /// Whether this expense has been archived
   final bool isArchived;
+  
+  /// URL to the receipt image (optional)
   final String? receiptUrl;
+  
+  /// List of expense splits showing how the cost is divided
   final List<ExpenseSplit> splits;
 
+  /// Creates a new [Expense] instance.
+  /// 
+  /// All parameters except [editedAt] and [receiptUrl] are required.
   const Expense({
     required this.id,
     required this.groupId,

lib/models/group.dart

@@ -1,14 +1,37 @@
 import 'group_member.dart';
 
+/// Model representing a travel group.
+/// 
+/// A group is a collection of travelers who are part of a specific trip.
+/// It contains information about group members, creation details, and
+/// provides methods for serialization with Firestore.
 class Group {
+  /// Unique identifier for the group
   final String id; 
+  
+  /// Display name of the group
   final String name;
+  
+  /// ID of the trip this group belongs to
   final String tripId;
+  
+  /// ID of the user who created this group
   final String createdBy;
+  
+  /// Timestamp when the group was created
   final DateTime createdAt;
+  
+  /// Timestamp when the group was last updated
   final DateTime updatedAt;
+  
+  /// List of members in this group
   final List<GroupMember> members;
 
+  /// Creates a new [Group] instance.
+  /// 
+  /// [id], [name], [tripId], and [createdBy] are required.
+  /// [createdAt] and [updatedAt] default to current time if not provided.
+  /// [members] defaults to empty list if not provided.
   Group({
     required this.id, 
     required this.name,
@@ -21,6 +44,12 @@ class Group {
         updatedAt = updatedAt ?? DateTime.now(),
         members = members ?? [];
 
+  /// Creates a [Group] instance from a Firestore document map.
+  /// 
+  /// [map] - The document data from Firestore
+  /// [id] - The document ID from Firestore
+  /// 
+  /// Returns a new [Group] instance with data from the map.
   factory Group.fromMap(Map<String, dynamic> map, String id) {
     return Group(
       id: id,

lib/models/trip.dart

@@ -1,20 +1,52 @@
 import 'dart:convert';
 import 'package:cloud_firestore/cloud_firestore.dart';
 
+/// Model representing a travel trip in the application.
+/// 
+/// This class encapsulates all trip-related information including dates,
+/// location, participants, and budget details. It provides serialization
+/// methods for Firebase operations and supports trip lifecycle management.
 class Trip {
+  /// Unique identifier for the trip (usually Firestore document ID).
   final String? id;
+  
+  /// Title or name of the trip.
   final String title;
+  
+  /// Detailed description of the trip.
   final String description;
+  
+  /// Trip destination or location.
   final String location;
+  
+  /// Trip start date and time.
   final DateTime startDate;
+  
+  /// Trip end date and time.
   final DateTime endDate;
+  
+  /// Optional budget for the trip in the local currency.
   final double? budget;
+  
+  /// List of participant user IDs.
   final List<String> participants;
+  
+  /// User ID of the trip creator.
   final String createdBy;
+  
+  /// Timestamp when the trip was created.
   final DateTime createdAt;
+  
+  /// Timestamp when the trip was last updated.
   final DateTime updatedAt;
+  
+  /// Current status of the trip (e.g., 'draft', 'active', 'completed').
   final String status;
 
+  /// Creates a new [Trip] instance.
+  /// 
+  /// Most fields are required except [id] and [budget].
+  /// [status] defaults to 'draft' for new trips.
   Trip({
     this.id,
     required this.title,

lib/models/user.dart

@@ -1,11 +1,27 @@
 import 'dart:convert';
 
+/// Model representing a user in the travel mate application.
+/// 
+/// This class encapsulates user information including personal details
+/// and provides methods for serialization/deserialization with Firebase
+/// and JSON operations.
 class User {
+  /// Unique identifier for the user (usually Firebase UID).
   final String? id;
+  
+  /// User's last name.
   final String nom;
+  
+  /// User's first name.
   final String prenom;
+  
+  /// User's email address.
   final String email;
 
+  /// Creates a new [User] instance.
+  /// 
+  /// [nom], [prenom], and [email] are required fields.
+  /// [id] is optional and typically assigned by Firebase.
   User({
     this.id,
     required this.nom,
@@ -13,7 +29,9 @@ class User {
     required this.email,
   });
 
-  // Constructeur pour créer un User depuis un Map (utile pour Firebase)
+  /// Creates a [User] instance from a Map (useful for Firebase operations).
+  /// 
+  /// Handles null values gracefully by providing empty string defaults.
   factory User.fromMap(Map<String, dynamic> map) {
     return User(
       id: map['id'],
@@ -23,13 +41,17 @@ class User {
     );
   }
 
-  // Constructeur pour créer un User depuis JSON
+  /// Creates a [User] instance from a JSON string.
+  /// 
+  /// Parses the JSON and delegates to [fromMap] for object creation.
   factory User.fromJson(String jsonStr) {
     Map<String, dynamic> map = json.decode(jsonStr);
     return User.fromMap(map);
   }
 
-  // Méthode pour convertir un User en Map (utile pour Firebase)
+  /// Converts the [User] instance to a Map (useful for Firebase operations).
+  /// 
+  /// Returns a map with all user properties for database storage.
   Map<String, dynamic> toMap() {
     return {
       'id': id,
@@ -39,15 +61,20 @@ class User {
     };
   }
 
-  // Méthode pour convertir un User en JSON
+  /// Converts the [User] instance to a JSON string.
+  /// 
+  /// Useful for API communications and data serialization.
   String toJson() {
     return json.encode(toMap());
   }
 
-  // Méthode pour obtenir le nom complet
+  /// Gets the user's full name in "first last" format.
   String get fullName => '$prenom $nom';
 
-  // Méthode pour créer une copie avec des modifications
+  /// Creates a copy of this user with optionally modified properties.
+  /// 
+  /// Allows updating specific fields while preserving others.
+  /// Useful for state management and partial updates.
   User copyWith({
     String? id,
     String? nom,
@@ -62,17 +89,22 @@ class User {
     );
   }
 
+  /// Returns a string representation of the user.
   @override
   String toString() {
     return 'User(id: $id, nom: $nom, prenom: $prenom, email: $email)';
   }
 
+  /// Compares users based on email address.
+  /// 
+  /// Two users are considered equal if they have the same email.
   @override
   bool operator ==(Object other) {
     if (identical(this, other)) return true;
     return other is User && other.email == email;
   }
 
+  /// Hash code based on email address.
   @override
   int get hashCode => email.hashCode;
 }